2 Mr, McKay, Notes on the Geology of the Coast [March 26, 



intrusive rocks — and the objections are admittedly great — there can 

 be little doubt that the band that forms Madagascar Beef is an 

 intrusive rock like an ordinary trap dyke. 



Between Madagascar Reef and the Keiskarama Eiver occurs the 

 most southerly dolorite rock known in the colony — marked No 1 on 

 map 2. In the Western Province the most southerly that is known is 

 about five miles to the south of Sutherland, in the division of 

 Fraserburg ; there it partakes more of a syenitic greenstone than of a 

 dolorite. It would be a matter of considerable interest to ascertain if 

 dyke No 1 and that at Sutherland have any connection with each other. 

 The direction is the same in both cases — 10 deg. north of true west. 

 To observers who travel by railway and take an interest in these 

 matters, I would recommend the following points for examination : — 



Ist — On the Beaufort West Railway — about ten miles north of 

 Beaufort West. 



2nd — Near the Bull River, Zwart Ruggens, on the Graaff-Reinet 

 Railway 



3rd — At the Little Fish River on the Cradock Railway. 



Between the Keiskamma and Chalumna Rivers and at Payne's 

 Drift,, at points marked by a cross on map 2, are bare patches of a 

 peculiar jaspery conglomerate containing pebbles of wood-opal, 

 calcedony, and other rounded fragments of foreign rock, set Jin a 

 matrix of liver-coloured jasper. The conditions of this rock have not 

 been satisfactorily ascertained ; but it is highly possible that it has 

 been an over-spreading mass of molten matter that has flowed over 

 the dicynodon rocks while they were in process of deposition. This 

 would, of course, make it older than the overl3dng shales and the 

 subsequently intrusive traps. The three points marked X on the map 

 are nearly on one level, and doubtless form one continuous sheet, pro- 

 bably an outflow from the neighbourhood of Mount Coke, where an 

 inextricable complication of almost every variety of erupted rocks 

 occurs. Part of the complication there may arise from the intersection 

 of dykes Nos. 4, 5, 6, 7, 8, 9, 10, 11 and 12. In addition to this, 

 however, it is inferred from the beds of laterite found that it must have 

 beeu the centre of a more recent and independent heat action. As it 

 would be impossible to indicate even a remotely accurate delineation 

 of thp rocks here without an expenditure of time and labour that is 

 not at th« command of the writer, the s])ace it should occupy on the 

 accompanying map has been left blank. Mount Elizabeth — one of the 

 three cone-like hills which form what is known as the district of Mount 

 Coke, is a core-like mass of trachyte, is more recent and quite uncon- 

 nected with the bewildering numbers of trap-dykes by which it is 

 surrounded. At Fort Grey, near East London, and at the Quintani 

 in the Transkei, bosses of a similar trachyte occur under the same 

 conditions. 



Dyke No. 8 is a very beautiful porphyrj', about 15 feet wide, of 

 a dark reddish-brown colour with crystals of pearly felspar, about a 

 quarter of an inch square, very regularly distributed through it. It 

 will, at some future day, be a stone of considerable value for architec- 

 tural purposes. 



About two miles to the south of dyke No. 15, and near Peelton, a 

 dyke crops up, the strike of which I have not been able to deter- 

 mine. It is composed of albite and hornblende, and is probably con- 

 uected with a dyke that occurs at the Izeli (King WiUiamstown divi- 



